This application is a 371 of PCT/EP99/00284 filed Jan. 19, 1999.
The invention relates to separation materials for planar chromatography which have porous separation medium layers of low thickness and are suitable for the separation of substances on the nL scale.
Increasing demands made of the performance of analytical methods, in particular in respect of speed and detection sensitivity, mean that in the case of thin layer chromatography (planar chromatography) there is a need for separation medium layers which are significantly thinner than those obtainable hitherto, i.e. thinner than 50 xcexcm.
Cremer and Nau (1968) describe experiments (Natur-wissenschaften 55, page 651) in which chromatographic separations were carried out on ultrathin layers. The layers used consisted of indium oxide, bismuth oxide or tin oxide and had a thickness of 1 xcexcm or less. These layers were vapour-deposited. The substances were able to be separated on model systems, but the method has not found further use. For thin layer chromatography, the practice has thus hitherto been to apply particulate separation media, which can have spherical or irregular shapes, to a support. In this procedure, it is possible to add auxiliaries such as binders, fluorescent indicators, reflection reinforcers or the like to the layer. Such additives are well known to those skilled in the art. In this method, it does not appear to be possible to reduce the thickness of the separation medium layer to less than 50 xcexcm.
It has been found that significantly thinner separation medium layers, for example layers having a thickness of about 10 xcexcm, can be produced using a completely different principle which has hitherto not been customary for the production of separation medium layers of silica gel for thin layer chromatography.
These processes and the separation materials for thin layer chromatography produced by means of these processes are provided by the present invention.
DE 19 08 695 discloses methods of applying thin coherent films of titanium dioxide and/or zirconium dioxide having a thickness of less than 1 xcexcm to plastic films. This is said to prevent impurities from the plastic getting into the separation medium layer. However, these layers of titanium dioxide and/or zirconium dioxide have no chromatographic activity.
The invention provides separation materials for thin layer chromatography consisting of a support and a separation medium layer obtainable by the following process steps:
a) cleaning of the support;
b) application of a liquid film comprising a polysilicic ester to a support;
c) introduction of the support with the liquid film into an atmosphere which effects hydrolysis and further polymerization of the polysilicic ester;
d) hydrolysis and further polymerization of the polysilicic ester at constant temperature;
e) washing of the silica layer;
f) drying of the silica layer.
The invention further provides separation materials having the features mentioned, whose silica gel surface is modified by means of separation effectors.
The invention also provides for the use of separation materials having the features mentioned for separation of at least two substances by thin layer chromatography.
Finally, the invention provides a process for producing separation materials, which comprises the following steps:
a) cleaning of the support;
b) application of a liquid film comprising a polysilicic ester to a support;
c) introduction of the support with the liquid film into an atmosphere which effects hydrolysis and further polymerization of the polysilicic ester;
d) hydrolysis and further polymerization of the polysilicic ester at constant temperature;
e) washing of the silica layer;
f) drying of the silica layer;
where, in preferred embodiments, the process step b) is carried out by spraying the solution onto the support or the liquid film is applied by firstly applying the liquid at one point and subsequently rotating the support around the point of application, with the axis of rotation perpendicular to the plane of the support, or by distributing the liquid film using a roller.